In order to control weeds in your Oklahoma lawn, apply pre-emergent twice per year—once in spring and once in fall. The timing for these applications is:
- Spring: February 1–March 15
- Fall: August 15–September 15
You will get the best results from your pre-emergent application by further pinpointing timing based on soil temperature, but these date ranges are good working guidelines for Oklahoma.
Why Pre-Emergent Timing is Important in Oklahoma
Pre-emergent herbicides provide the biggest benefit when they are timed optimally. They work by entering the soil and remaining there for up to 6 weeks. During this time, they kill any seed that germinates underground.
Pre-emergent won’t kill dormant seeds or weeds that have already come up. If you apply too early, you’ll waste your pre-emergent on soil full of dormant seeds. If you apply too late, the weeds will have already broken the soil’s surface and pre-emergent won’t kill them.
- Pre-emergent only kills seeds as they actively germinate (sprout) underground.
- Pre-emergent does not kill dormant seeds or weeds that have already established themselves.
- After application, pre-emergent is active for 6 weeks.
- To maximize effectiveness, time pre-emergent application just before weed seeds begin to germinate.
When timed correctly, pre-emergent stops broadleaf weeds and grassy weeds in their tracks. It’s a very powerful tool to stop the annual weeds that plague Oklahoma yards.
Spring Pre-Emergent Timing for Oklahoma
Although the date range of early February through mid-March is a good ballpark for applying spring pre-emergent throughout Oklahoma, the best way to pinpoint your pre-emergent timing is by monitoring soil temperature and applying accordingly. Here’s how:
- Typical application timing is from February 1 through March 15.
- Spring weeds begin to germinate as soil temperatures (not air temperatures) climb toward 55℉.
- Monitor soil temperatures in your region with this online soil temperature map.
- Once soil temperatures have risen to 55℉ for 2–3 consecutive days, it’s time to spread pre-emergent.
- This will ensure 100% of your pre-emergent’s 6-week lifespan is used to combat spring and summer annual weeds.
As a rule of thumb, soil temperatures are usually 10 degrees cooler than daytime air temperatures. This calculation is less accurate than a soil temperature map, but can be used in a pinch.
Fall Pre-Emergent Timing for Oklahoma
Annual bluegrass is a wintertime blight on many Oklahoma yards, but it’s not alone. Henbit and common chickweed are also habitual fall invaders. A second application of pre-emergent herbicides will stop these annual weeds.
- Average application timing between August 15 and September 15
- Winter annuals begin to germinate as soil temperatures fall toward 70℉ at the end of summer.
- Optimal fall pre-emergent timing is when soil temperatures dip down to 70℉ for 2–3 consecutive days.
Whatever type of weed or invasive grass you’re up against, a well-timed pre-emergent application in the fall will keep your lawn weed free through fall and winter.
What is the Best Pre-Emergent Herbicide for Oklahoma Lawns?
In Oklahoma, most lawns are planted with warm-season grasses. Therefore, it’s essential to choose a pre-emergent that is optimized for warm-season grasses and the weeds that grow in the region. Barricade and Prodiamine WDG are two of the best choices for lawn care in Oklahoma.
- Choose a pre-emergent formulated for warm-season lawns.
- Avoid products that contain Atrazine unless your lawn is St. Augustine, Centipede, or Zoysia grass. Atrazine will harm other turfgrass types, like Bermuda grass.
- Apply pre-emergent according to product label rates.
In order to maximize pre-emergent effectiveness, follow manufacturer instructions for application rates. Do not overapply pre-emergent. Herbicides applied at excessive levels can harm turf grasses.
Should You Mow Before Applying Pre-Emergent?
Pre-emergent needs to make contact with the soil so it can be absorbed once you water it in. Mowing your lawn to 1.5–2 inches in height before applying pre-emergent allows more of the herbicide to reach the soil and yields better results stopping broadleaf weeds and grassy weeds.
- Mow grass lower than normal (1.5–2 inches) prior to spreading pre-emergent.
- Check your lawn’s thatch layer. If it’s thicker than 0.5 inches, dethatch to allow pre-emergent to reach the soil.
- The more easily pre-emergent reaches the soil, the more effective it will be.
Thick thatch works as a barricade that prevents pre-emergent herbicides from reaching the ground. Dig up a small section of your yard and measure the thatch layer. If it’s more than 0.5 inches thick, it’s time to dethatch. Mowing and dethatching will make your pre-emergent application far more effective.
Do You Need to Water in Pre-Emergent?
Watering in pre-emergent is essential in order to put it to work in your yard. If your pre-emergent comes in granule form, it must be watered in to dissolve it and allow it to break down.
- Watering pre-emergent allows it to dissolve and penetrate the soil.
- After application, water pre-emergent into the soil with 0.5 inches of water.
- 30–60 minutes with this automated sprinkler system will water in pre-emergent the correct amount.
If you are using a liquid pre-emergent or granules that you dissolve in water before application (such as Prodiamine WDG) then you may not need to water following application. Review product label guidelines.
- Waters your lawn automatically the whole season.
- Eliminates constant hassling with hose and sprinkler adjustments.
- Sprinklers retract into the lawn for a clean, uncluttered appearance and easier mowing.
- Wind-resistant Rain Curtain nozzle technology reduces overspray and saves water.
- Avoids overwatering with easy-to-set schedules that help you meet the moisture needs of your yard.
How Long Does it Take for Pre-Emergent to Work?
Once your pre-emergent has been applied and watered in, it will begin to work. Remember, with pre-emergent the best results will be invisible. Under the surface of your Oklahoma lawn, the pre-emergent will attack seeds as they attempt to sprout. If you’re not seeing new weeds, the pre-emergent is working.
- Pre-emergent begins working immediately after being watered into the soil.
- Pre-emergent will kill germinating seeds below ground for approximately 6 weeks.
A correctly timed and applied pre-emergent will stop broadleaf weeds, annual bluegrass, and grassy weeds for 6 weeks. A spring application will stop summer weeds, and a fall application will make sure winter annuals don’t sprout.
What is the Best Time to Apply Pre-Emergent in Oklahoma?
To stop summer annual weeds, apply pre-emergent to your Oklahoma yard in early spring, between February 1 and March 15, once soil temperatures rise to 55℉.
To halt winter annual weeds, plan your pre-emergent herbicide application between August 15 and September 15, when soil temperatures fall to 70℉.
These two applications will stop all types of weeds, from invasive spring weeds, to ugly winter weeds. The result of using a few well-timed herbicides is a beautiful Oklahoma lawn free of grassy and broadleaf weeds.